Block copolymers of various structures have been known for some time. Commonly, two or more blocks are combined in a single polymer which possesses different physical and/or chemical character to make a material having properties that are some combination of those individual blocks. In this way, mono-alkenyl arenes and conjugated dienes have been employed as monomers for such blocks prepared by anionic polymerization. The glassy blocks comprising mono-alkenyl arenes provide physical strength and the rubbery blocks comprising conjugated dienes provide an elastomeric character. When arranged in the proper structure such block copolymers, often generically referred to as styrenic block copolymers, form thermoplastic elastomers.
U.S. Pat. No. 3,670,054 to De La Mare et al. disclosed block copolymers that have a reduced sensitivity to organic solvents. In particular the block copolymers disclosed include hydrogenated (polybutadiene-polystyrene-polyisoprene-polystyrene-polybutadiene). In addition to possessing the glassy character of polystyrene and the rubbery character of polyisoprene, these block copolymers also possessed some character typical of semi-crystalline polymers since the hydrogenated polybutadiene blocks resembled polyethylene.
U.S. Pat. No. 4,107,236 to Naylor et al. discloses a hydrogenated block copolymer having the structure low vinyl butadiene block-polystyrene block-hydrogenated medium vinyl butadiene block-polystyrene block-hydrogenated low vinyl butadiene block (lvB-S-mvB-S-lvB). Upon hydrogenation, the low vinyl butadiene blocks (lvB) become semi-crystalline polyethylene and the medium vinyl butadiene block (mvB) becomes ethylene/butylene rubber.
U.S. Pat. Publ. No. 2010/0056721 to Wright et al. discloses selectively hydrogenated linear or radial styrenic block copolymers having terminal semi-crystalline blocks resulting from the hydrogenation of low vinyl butadiene blocks. The block copolymers were used neat or in melt-processed compounds for a variety of film, fiber and molding applications.
Polymeric additives have been used in drilling and well stimulation and completion fluids. The desired rheological characteristics of a hydrocarbon fluid are described in Legget, C. Svaboda, M. Arvie, Jr, R. Horton, J. Zhang, “Oil-Based Insulating Packer Fluids”, U.S. Pat. No. 7,863,223, dated Jan. 4, 2011. This packer fluid is a hydrocarbon fluid and a gelling agent. The packer fluid has a yield power law characteristic, and includes a polyamide component.
U.S. Pat. No. 8,188,014 to Svoboda describes a polyamide polymer mixed with oleaginous fluid for use in oilfield application for in-situ solidification in the annular barrier of a well.
Styrenic block copolymers have found a number of applications in drilling, well stimulation and completion. U.S. Pat. No. 6,017,854 to Van Slyke describes oilfield fluids containing styrenic block copolymers in petroleum derived or synthetic hydrocarbon fluid. The styrenic block copolymers are typically SBS or SIS triblock copolymers.
Selectively hydrogenated styrenic diblock copolymers such as polystyrene-hydrogenated polyisoprene (i.e. S-EP) have found application as viscosifiers in oilfield fluids. However, these diblock types of styrenic block copolymers can be difficult to handle because of their tendency to agglomerate into a single mass. This behavior is known as “blocking” and is not to be confused with the “block” character of the copolymers. Blocking refers to the agglomeration of the solid polymer particles. To mitigate this problem, various dusting agents have been applied to the surface of finished diblock copolymer pellets, strands, and crumbs. Usually, significant amounts of these solid dusting agents must be used to exhibit an appreciable effect. Although solids are acceptable in some applications, in many cases it is desirable to avoid the inclusion of solids in oilfield fluids. In order to eliminate all solids, undusted polymers must be used. Such undusted diblock copolymers may exhibit a strong blocking tendency requiring undesirable applications of force to break apart these undusted, agglomerated polymers.
Additionally, the viscosities of oilfield fluids, particularly at lower temperatures, can be quite high. While in specific situations and wellbore locations high viscosities are required, fluids having a high viscosity generally require more energy to be pumped. This can lead to high back pressures which, in turn, can result in formation damage. A fluid that exhibited a high viscosity only after being placed in the desired location in the wellbore but remained as a low viscosity fluid until that time would be especially advantageous for applications such as packer fluids. In this situation, the oilfield fluids would be easily pumpable and would possess the high viscosities required of packer fluids only after being placed into the well at the locations where they are needed.
Thus, it is desirable to produce a block copolymer useful in oilfield fluid applications which did not introduce solid particulates and yet did not block/agglomerate, but remained free-flowing.